Partner Peter Todd said: "Thousands of parents have been left in a desperate position of watching their children deteriorate with this life-shortening condition, while knowing that there is a drug out there that can help improve their health and extend their lives."

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But the National Institute for Health and Care Excellence (Nice), which decides which treatments should be available on the NHS in England and Wales, says it is too expensive for the health service to provide.

The drug is already available in several European countries after being approved by the European Medicines Agency in 2015.

Katie Stafford, of Totnes, Devon, who has cystic fibrosis

NHS bosses have been engaged in years of negotiations with Orkambi's manufacturer Vertex Pharmaceuticals to secure an affordable deal.

This is despite the Government's claims that the company was offered the "largest ever" financial commitment in the history of the NHS.

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Earlier this year, health ministers wrote to the company urging it to drop Orkambi's price, saying "time was of the essence" for cystic fibrosis patients.

Katie Stafford, of Totnes, Devon, who has cystic fibrosis

A petition signed by more than 100,000 people also triggered a debate on the issue in Parliament this year.

MPs on the Commons Health and Social Care Committee leading an inquiry into the patients' access to drugs, have threatened to publish the details of negotiations between Vertex, Nice and NHS England if a deal is not reached by November 30.

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A spokesman for the Department for Health and Social Care said: "Despite being offered in the region of £500m over five years, the largest ever commitment of its kind in the 70-year history of the NHS, Vertex has refused to accept, putting Orkambi out of reach of patients.